根据sessionId获取session

import java.util.HashMap;

import javax.servlet.http.HttpSession;

/**
 * session
 * @author dev_xiao
 *
 */
public class MySessionContext {
	private static HashMap mymap = new HashMap();

    public static synchronized void AddSession(HttpSession session) {
        if (session != null) {
            mymap.put(session.getId(), session);
        }
    }

    public static synchronized void DelSession(HttpSession session) {
        if (session != null) {
            mymap.remove(session.getId());
        }
    }

    public static synchronized HttpSession getSession(String session_id) {
        if (session_id == null)
        return null;
        return (HttpSession) mymap.get(session_id);
    }
}

　　监听文件

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * session
 * @author lixiao
 *
 */
public class MySessionListener implements HttpSessionListener {
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
    MySessionContext.AddSession(httpSessionEvent.getSession());
    }

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        HttpSession session = httpSessionEvent.getSession();
        MySessionContext.DelSession(session);
    }

}

　　配置web.xml

<listener>
　　<listener-class>com.tonbusoft.uums.commons.MySessionListener</listener-class>
</listener>